With Beijing's air quality index returning to acceptable levels -- if you can call a measurement between "very unhealthy" and "hazardous" acceptable -- the capital's beleaguered residents can resume life as normal. Yet an exceptional stretch of atrocious air produced an unexpected silver lining: the Chinese media covered the event with unusual transparency.

Typically, the Chinese press tries to put the best possible spin on Beijing's notorious pollution problem, questioning the accuracy of air-quality measurements and dismissing the concerns as "fog". Yet as many pundits -- including our own James Fallows -- have noticed, the national media has reacted to "airpocalypse" with a startling frankness. What has caused this shift?

One explanation may be China's history of dealing with Severe Acute Respiratory Syndrome, or SARS, an epidemic which struck the country in late 2002. After several months of obfuscation, Beijing succumbed to international pressure and allowed its media to report the story openly. This free-flow of information startled the outside world and led the normally staid editors at The Economistto wonder if SARS was "China's Chernobyl". The current pollution crisis, which has caused no known fatalities, is nowhere near as grave as SARS. Nevertheless, the candor with which the bad air is being reported may reflect a blueprint established during the earlier crisis.

A second explanation may lie with the man at the top of China's government hierarchy: incoming president Xi Jinping. Xi is thought to be a relative liberal in the context of Chinese politics, and speculation is rife that the incoming leader will press for significant reforms during his years at the helm. Though not yet officially the nation's president -- his stodgy predecessor Hu Jintao will hang on until March -- Xi may have already flexed his muscles by ordering China's propaganda czars to go easy on the media.

Both explanations, though, have significant flaws. China's relative openness with the SARS crisis came to an abrupt end during the country's next major health crisis, the tainted milk scandal of 2008. When hundreds of thousands of children fell ill after drinking milk laced with melamine, the Communist Party ordered the media to downplay the issue. The difference between the SARS and melamine crises was clear: while the former became an international issue for the very fact that diseases don't respect borders, the latter was contained inside China and thus not subject to the same degree of media scrutiny. As Jeremy Goldkorn, a prominent business consultant and media critic based in Beijing said via e-mail, "The government's default mode is still to cover up rather than reveal".

Likewise, there's little evidence that Xi Jinping will preside over a true liberalization of China's media. Chinese journalists still work under threat of intimidation and violence from government officials, even when covering stories that lack an explicitly political angle. And even if Xi harbored reformist ambitions, he may lack the political capital to navigate China's treacherous political landscape. Preserving the status quo, as always, remains the most palatable option for any Chinese leader- particularly one so new to the job.

Why, then, would the Chinese government allow such candor on the pollution question? Social media plays a role. Prominent Beijing real estate developer Pan Shiyi regularly tweets information about pollution to his several million followers on Sina's Weibo, and the flurry of similar comments by more ordinary users has brought the pollution issue into the open. At a basic level, the government understands that once an issue hits critical mass, there's little point in perpetuating the myth any further.

Also, unlike other issues which threaten the Chinese government's hold on power, environmental concerns do not discriminate by class or income level. While many of Beijing's citizens may not pay attention to esoteric political issues, the Communist Party surely believes that pollution has the potential to unite a large number of people against its governance. That, more than anything else, may explain why the government has approached this issue with unusual openness.